Activists "Letzte Generation" (Last Generation) said its members had entered four German airports -- Cologne-Bonn, Nuremberg, Berlin and Stuttgart -- unfurling banners reading "Oil kills".

"A total of eight people entered the runways as early as 5:00 am and stuck themselves to the asphalt," the climate organisation said in a statement.

They did not enter the runways.

But airport operators in the Nuremberg and Cologne-Bonn airport said that air traffic had still been suspended due to ongoing police operations.

In Berlin and Stuttgart, the people stuck on the runway were quickly removed by police and air operations were not affected, police and airport sources told AFP.

Last Generation is known for mounting eye-catching protests -- from throwing mashed potatoes at paintings in museums to glueing themselves on busy roads.

In July activists from the group halted traffic for two hours during the busy summer holiday season by gluing themselves to the tarmac at Germany's busiest airport, Frankfurt.